Editing Module:Buffer/doc (section)

===Mapping process===
Tables are mapped in two stages.

The initial stage is a {{luaref|for|numerical for loop|y}} which inserts integers between {{code|lang=lua|1}} and {{code|lang=lua|#table}} in the number key map. Because nothing is checked in this step, this may map keys which the [[#Iterators|numeric map iterator]] would pair with nil values or with values from the table's {{luaref|Metatables|meta __index|y}}.

The second stage explores the table's keys with an {{luaref|iterators|iterative for loop|y}} and {{luaref|next|next, table}} as the default ''expression-list'', or, if ''ext'' evaluates true, the expression returned by {{code|lang=lua|ext( table )}}. This ignores keys already mapped in the first stage and checks if any unmapped key is a number before indexing it in the appropriate map group. Upon completion, if any new number key were found in the second stage, this runs the numeric map through {{luaref|table.sort||y}}. No order is imposed on the non-numeric map.

Alternatively, a table may qualify for "mapless" iteration if {{luaref|rawget|args=table, 1}} is not nil, and {{luaref|next|args=table, #table}} returns nil. If either ''flag'' or ''ext'' are not nil, or if the table was previously mapped, such permanently disqualifies a table for mapless processing.

As a side note, if mapless numeric iteration occurs, this returns {{code|lang=lua|iterator, table, nil}}. In other words, you may use {{luaref|select}} to confirm that the table qualifies for mapless iteration when it has a third explicit return (for debugging).